Studies of mobilities of specific cell surface components and their interactions with the cell interior and various effectors will continue. Methods of fluorescence photobleaching recovery will be applied to various animal cell systems including macrophage, normal and dystrophic muscle, erythrocytes, and fibroblasts. Interactions of enveloped virus with the cell membrane, fibronectin distribution on the cell surface relative to cytoskeleton and low density lipoprotein distribution on the cell surface are included in the problems to be studied. A new apparatus for the measurement of local deformability of cultured cells in being developed.